Proton magnetic resonance (“MR”) spectroscopy (“1H-MRS”) uses selective excitation of a volume of interest (“VOI”) for localization, and to prevent aliasing in spectroscopic imaging (“1H-MRSI”). (See, e.g., References 1-5). Two known and commonly used VOI excitation modules use three orthogonal spatially-selective pulses: 90°-180°-180° Point Resolved Spectroscopy (“PRESS”) (see, e.g., Reference 1), or 90°-90°-90° Stimulated Echo Acquisition Mode (“STEAM”). (See, e.g., Reference 2). The three pulses generate nine transverse coherence pathways: three free induction decays (“FID”), four spin echoes (“SE”) and two stimulated echoes (“STE”). (See, e.g., References 6 and 7). Judicious use of gradient spoiling can dephase all the pathways that originate from spins outside the VOI, which can result in an excellent rejection of outer volume contamination. (See, e.g., References 8, 9). PRESS and STEAM each refocus a single coherence pathway: the double spin echo (e.g., in PRESS) or one of the stimulated echoes (e.g., in STEAM), both of which originate from spins within the VOI.
For a given peak radio-frequency (“RF”) power and specific absorption rate (“SAR”), STEAM's 90° pulses can offer several advantages over PRESS's 180° pulses: (i) SAR that can facilitate the reduction of the recycle time (“TR”) to improve the signal-to-noise-ratio (“SNR”)/unit-time (see, e.g., Reference 10); (ii) higher pulse bandwidths, which can lead to smaller chemical shift displacement (“CSD”) (see, e.g., Reference 11); (iii) shorter echo times (“TE”), suffering less T2 and J-coupling losses; and (iv) improved immunity to B1+ variations. These, however, can come at a cost of about half the SNR per scan. (See, e.g., Reference 9). Since the metabolites' signals can be 4-5 orders of magnitude weaker than the water used in magnetic resonance imaging (“MRI”), the SNR advantage of PRESS can trump STEAM's advantages, and can be the method of choice for 1H-MRS experiments. PRESS's higher CSD in the two 180° pulse directions can be mitigated with high bandwidth refocusing pulses designed using, for example, optimal control theory (see, e.g., References 12 and 13), or the Shinnar-Le Roux procedure (see, e.g., Reference 14), but at a cost of increased SAR, which can become prohibitive when attempting to keep the same CSD. The spatial B1+ variability can be addressed with adiabatic pulses, for example, SADLOVE (see, e.g., Reference 15) or LASER (see, e.g., References 16, 17 and 18), but their double-refocusing can prolong the minimum TE, and can increase SAR. The longer TE can attenuate signals of J-coupled metabolites that can often have short T2s, while their higher SAR can prolong the repetition time, thereby reducing the SNR/unit-time.
While both PRESS and STEAM can select a single, particular coherence, pathway, there can be compelling advantages to combining multiple pathways. For example, solid and liquid state nuclear magnetic resonance (“NMR”), pulse sequences such as HNCA, TOCSY-HSQC and MQMAS, can combine different pathways for increased sensitivity (see, e.g., References 19-21), whereas multi-pulse MR imaging sequences can refocus multiple coherence pathways to generate contrast and boost sensitivity (see, e.g., Reference 22), or to simultaneously obtain maps of several parameters. (See, e.g., Reference 23). Similarly, refocusing the spin and stimulated echo pathways for efficient T1 mapping has been suggested recently for echo planar 1H-MRSI. (See, e.g., Reference 24).
An exemplary three-pulse 1H-MRS localization paradigm can be modified by adjusting the three RF pulses' phases, flip angles, timings, and coherence selection gradients, in order to acquire both the double-spin and one of the stimulated echo pathways, this exemplary procedure can be denoted as STRESS (e.g., STEAM+PRESS). Utilizing the maximal B1+ immunity can yield a family of STRESS sequences, parameterized by a (e.g., the flip angle of the first RF pulse). The B1+ immunity can be shown to be superior to that of both PRESS and STEAM for most values of α. Results can be shown in a phantom and a healthy volunteer at 3 T for the 110°-108°-108° member of the STRESS family, which retains 83%-100% of the PRESS SNR (e.g., metabolite dependent) at only 75% of its SAR, and about 33% of its in-plane CSD for equal TE and TR, while also offering a shorter minimum echo time of, for example, TE=26.6 ms compared to PRESS's TE=40 ms.
Thus, it may be beneficial to provide an exemplary system, method and computer-accessible medium that can be used to, for example, simultaneously acquire a stimulated echo and a double spin echo, and which can overcome at least some of the deficiencies described herein above.